Polymeric compositions and methods of using them

ABSTRACT

Water-immiscible liquids, for example oil-based drilling fluids, are thickened by the addition of an aqueous dispersion of polymeric particles that are water-insoluble, and insoluble but swellable polymer, in the water immiscible liquid. The particles have a unswollen average diameter of less than 10 μm and at least 30% by weight are preferably in the range 0.5 to 5 μm. Preferred polymers are formed from more than 80% by weight hydrophobic monomers, preferably alkyl (meth) acrylates, and up to 20% hydrophilic monomers, preferably unsaturated carboxylic acids, preferably acrylic acid.

It is well known to thicken a liquid by addition of a polymericviscosifier. In some instances it is desired to obtain viscosity that isresistant to applied shear but in many instances it is desired to obtaina viscosity that reduces with applied shear, i.e., a shear thinningcomposition. This is particularly useful in, for instance, drillingfluids and other compositions for use downhole.

When the liquid is aqueous, the viscosifier is often a water solublepolymeric material. It may be a natural, modified natural or syntheticpolymer, for instance hydroxyethyl cellulose or high molecular weightpolyacrylic acid. In U.S. Pat. No. 4,059,552, Zweigle proposed that anaqueous medium could be given high viscosity that is resistant to highshear by the use, as viscosifier, of micro beads having a size 0.2 to 4microns and that are of a water insoluble, water swellable polymerformed of water soluble vinyl monomer with a specified amount of crosslinking agent. In the examples, Zweigle forms polymers of acrylamide,often with sodium acrylate, by reverse phase polymerisation in thepresence of a cross linker.

When the liquid that is to be thickened is a water immiscible liquid,for instance a hydrocarbon, the viscosifier is usually soluble in theliquid. For instance in EP No. 22982 mineral spirits are thickened bydissolving a particular acrylate copolymer therein. In ChemicalAbstracts Vol. 78 30364Z, the viscosity of toluene is increased bydissolving into it a copolymer of isobutylmethacrylate with methacrylicacid. In Chemical Abstracts Vol. 83 134617D, it is proposed to dissolvevarious other polymers, including butadiene styrene polymer, in mineraloils to increase viscosity. The use of natural rubber latex in benzeneis proposed for increasing viscosity of lubricating oil in ChemicalAbstracts Vol. 82 17587N.

In GB No. 2003904, it is proposed to thicken an organic solvent bydissolving therein a copolymer of certain hydrophobic and hydrophilicmonomers. The polymer must be such that it is soluble in the solvent andhas a glass transition temperature of at least 30° C. Most of theexamples show satisfactory copolymers of 99 parts isobutylmethacrylatewith 1 part methacrylic acid but the examples also show that theseproportions can lead to unsatisfactory copolymers, depending upon thepolymerisation conditions. A wide variety of possible monomers arementioned in the specification but many of them are clearly unsuitablefor use as the main component of the polymer as they would give a verylow glass transition temperature, far below the specified minimum of 30°C. The polymers may be made by bulk, suspension or, preferably, emulsionpolymerisation and the polymer is separated as a dry product.

It is generally desired for soluble polymer thickeners to have thehighest possible molecular weight as this increases their thickeningeffect but the viscosity attainable by the use of such polymers is stillrather low.

In EP No. 106528, it is said that a latex of a neutralisedsulphonate-containing styrene polymer can be used as a viscosifier in anoil-based drilling mud and that the addition of a polar cosolvent can beadded to increase the solubility of the sulphonated polymer. Thedescribed products are copolymers of styrene and styrene sulphonatecontaining 18 to 100 meq sulphonate groups per 100 grammes of polymer.It is stated that the latex can be used as an emulsion or the polymercan be precipitated from the latex prior to use.

Doverstrand Limited of Harlow, Essex, England in their publications POL050 and 051 September 1983 describe products under the trade namesPolymul HV and Polymul LV. These products are each said to be aqueouspolymer dispersions of inert hydrocarbon polymer that is soluble orswollen by aliphatic or aromatic solvents. They are each said to befluid loss reducers in oil muds and Polymul HV is also described as asecondary viscosifier. However the data in POL 050 shows that it is aninferior viscosifier compared to organophilic clay, amine treatedlignite, and asphalt. Although these products are apparently swellableby certain aliphatic or aromatic solvents, it appears that theirswellability in oil based drilling muds is inadequate, their particlesize is mainly below 0.5 μm and their viscosifying properties are poor.

In GB No. 2,131,067, which was published after the priority date of thepresent application, there are described natural rubber latices andother aqueous dispersions of polymers which are preferably hydrocarbonpolymers or comprise a major proportion of copolymerised hydrocarbon.The polymers are said to dissolve in oil or swell highly in the oil. Itis said that if the polymer is obtained in the form of a fine particledispersion it is desirable to agglomerate this since coarse particleemulsions are preferred to fine particle emulsions. In one example, acopolymer of 55 parts 2-ethyl hexyl acrylate and 45 parts vinyl acetateis used as a fluid loss additive in an aqueous mud.

Despite the many proposals to thicken water immiscible liquids, forinstance the oil phase of drilling muds, by polymeric viscosifiers, noneof them have been found to compete satisfactorily with, for instance,amine modified bentonite. In particular, none have been found to havethe desired combination of good viscosification with the desired shearthinning properties and the required thixotropy giving gel strength forparticle support that are particularly desired in, for instance,drilling muds and oil-based paints.

In the invention, a water immiscible liquid is thickened by a polymericviscosifier that comprises water insoluble polymer particles having adry, weight average, particle size of below 10 μm and that are insolublein the water immiscible liquid but that are swollen substantially by theliquid. Preferably at least 30% by weight of the particles are above 0.5μm.

Thus in the invention it is essential that the particles do not dissolvebut instead retain a discrete particulate structure. For the particlesabove 5 μm this structure can easily be observed using an opticalmicroscope.

The particles must swell substantially in the liquid and in practicethis means that their swollen volume should generally be at least 4times, and usually at least 6 times, their dry volume. If they swell somuch that the polymer tends towards full solubility, the benefits of theinvention may be lessened and so generally the particles do not swell bymore than 30 times, or at the most 50 times, their dry volume. Bestresults are generally obtained when the particles swell by from 10 to 25times their dry volume.

The viscosifying properties are partly due to the imbibition andimmobilisation of liquid in the swollen particles and partly due toparticle-particle interactions and so the specified small particle sizeis essential. The weight average particle size is preferably below 5 μmbut is normally above 0.02, preferably above 0.05, μm. Best results aregenerally achieved with a weight average particle size of from 0.1 to 2micron. Preferably at least 80%, and most preferably at least 90%, byweight of the particles have a size below 10 μm, preferably 0.05 to 5 μmand most preferably 0.1 to 4 μm.

The particles that contribute most effectively to the viscosifyingeffect appear to be those that are above 0.2 μm preferably above 0.4 μm,and generally below 10 μm, preferably below 5 μm. Preferably at least30%, most preferably at least 50% by weight of the particles are in thesize range 0.3 to 5, most preferably 0.5 to 3 or 4 μm. Dispersionshaving these size ranges are new.

The polymers are best made by dispersing polymerisable monomer ormonomers in a liquid in which they are substantially insoluble andpolymerising the monomer or monomers in that liquid to form a dispersionin the liquid of polymer particles having the desired particle size.This particle size can be controlled in known manner, for instance byappropriate choice of emulsifier and the amount of emulsifier. Theprocess is conveniently referred to as emulsion polymerisation since thefinal particle size is always small.

The liquid in which the emulsion polymerisation is conducted isgenerally water and so the resultant dispersion is a dispersion ofparticles in a continuous aqueous phase. The water may include variousadditives to improve physical properties. For instance, ethylene glycolmay be included to improve freeze-thaw stability.

At least 20, usually at least 30 and preferably at least 50%, by weightof the recurring groups in the polymer should be polar, and thus whenthe polymer is made by copolymerisation of monomers at least 50% byweight of the monomers should be polar monomers. This is surprisingsince the water immiscible liquid is generally non-polar. By referringto polar monomers in groups we mean groups having a significantpolarity, generally caused by the inclusion of a carboxylic and/or amidegroup substitute on to a hydrocarbon backbone. The presence of asubstantial proportion of polar groups in the polymer within thenon-polar or other water immiscible liquid appears to promote theparticle-particle interactions in a beneficial manner.

The presence in the polymer of a high proportion of aromatic hydrocarbongroups tends to make it difficult, or impossible, to obtain the desiredcombination of particle-particle interaction, insolubility andswellability and so the monomers from which the polymer is formed shouldnot contain above 30% aromatic hydrocarbon monomers and preferably aresubstantially free, and most usually totally free, of aromatichydrocarbons.

Although it appears necessary to include polar monomers for bestresults, it is necessary that at least most of the polar monomers arehydrophobic, as otherwise the polymer will be water soluble and/ornon-swellable in the water immiscible liquid. However the presence of asmall amount of hydrophilic monomers appears desirable. By hydrophilicwe mean that the monomer has a solubility of above 3% by weight in waterat room temperature and by hydrophobic we mean that it has solubility ofbelow 3% by weight in water at room temperature (20° C.). The preferredpolymers are formed from 0 to 20% by weight hydrophilic monomers, 25 to100% by weight polar hydrophobic monomers and 0 to 75% by weightnon-polar hydrophobic monomers. If the amount of non-polar hydrophobicmonomer is above 30%, then it will generally consist of ethylene andpreferably the only non-polar hydrophobic monomers included in thepolymers of the invention is ethylene. Best results are generallyobtained when the amount of polar hydrophobic monomers is from 50 to100%, most preferably 80, and often 90, to 100% by weight.

Suitable polar hydrophobic monomers include alkyl (meth) acrylates, themonoesters or diesters of dibasic ethylenically unsaturated acids suchas alkyl itaconates, alkyl maleates (e.g., the half ester of stearylalcohol with maleic anhydride) and alkyl fumarates and vinyl esters oflong chain acids, such as vinyl stearate, laurate and versatate.Hydrophobic N-alkyl substituted (meth) acrylamides may be used.Preferably at least 50% by weight, and most preferably at least 80% byweight of the monomers are (meth) acrylic monomers, generally alkylacrylate monomers. The hydrophobic monomers preferably include an alkylgroup that contains up to 30 carbon atoms, preferably 6 to 18 and mostpreferably 6 to 10 carbon atoms. Particularly preferred are copolymersof 90 to 100% by weight C₁₋₃₀ alkyl (meth) acrylate and 0 to 10% byweight hydrophilic monomer, especially those wherein the polymercontains 40 to 100% by weight C₆₋₁₀ alkyl acrylate.

A particularly preferred monomer is 2-ethyl hexyl acrylate. Valuablepolymers are formed from 40-100% of this, 0-10% hydrophilic groups andother C₆₋₃₀ alkyl (meth) acrylate, preferably 0-50% C₁₂₋₁₈ alkyl (meth)acrylate.

Other polar hydrophobic monomers that may be used include vinyl acetate,for instance copolymerised with ethylene and/or vinyl versatate.

The polymer particles used in the invention preferably have a relativelyhydrophilic coating as this seems to promote particle-particleinteractions within the water immiscible and generally non-polar liquid.The hydrophilic coating may be an external coating of, for instance, anemulsifier or some other material present during the polymerisation butpreferably is formed by copolymerisation of hydrophilic monomer. Thehydrophilic monomer may be any monomer that will provide polar oxygencontaining or nitrogen containing groups on the surfaces during thepolymerisation or in some other way. Suitable hydrophilic comonomersthat may be used include dialkyl amino alkyl (meth) acrylates and theirquaternary addition and acid salts, acrylamide, N-(dialkyl amino alkyl)acrylamide and meth acrylamides and their quaternary addition and acidsalts, hydroxy alkyl (meth) acrylates and sulphonic acids such as vinylsulphonic acid (as the free acid or, preferably, the alkyl amino salt)or unsaturated carboxylic acids such as methacrylic acid or, preferablyacrylic acid, generally as the free acid but possibly as an alkyl aminosalt. Other preferred monomers include hydroxyethyl (or propyl)acrylate, acrylamide and dimethylaminoethylmethacrylate (generally as aquaternary salt).

If the hydrophilic monomers are present in too great an amount, it maydifficult to obtain the desired small particle size. Accordingly theamount of the hydrophilic polymer is generally below 20% and preferablybelow 5%. The amount is normally at least 0.05%, preferably at least0.1% and most preferably at least 0.5%. Particularly preferred polymersare those obtained using acrylic acid, preferably in an amount of 0.3 to3%, as a copolymer with other monomers that are mainly alkyl (meth)acrylate, preferably mainly C₆₋₁₀ alkyl acrylate monomers.

The polymers useful in the invention preferably have a glass transitiontemperature (Tg) below about 25° C., often below 10° C. and mostpreferably below 0° C. Best results are generally obtained when Tg isbelow -20° C., most preferably in the range -40° to -70° or -75° C.

The polymers used in the invention are preferably film forming at 20°C., that is to say if the dispersion of the polymer is cast on a surfaceat room temperature the polymer will form a film.

The preferred polymers have >30% particles in the range 0.5 to 5μ, arefilm forming at 20° C., swell to at least 4 times, preferably 10 to 20times, their volume in the water immiscible liquid, and are formedmainly of hydrophobic polar monomers, optionally with ethylene, andpreferably with 0.2 to 5% of a water soluble, hydrophilic, monomer.Emulsions containing these are novel.

The polymer particles preferably remain in the aqueous dispersion inwhich they are formed prior to incorporation with the water immiscibleliquid and should not be dried or otherwise separated from thedispersion. With the preferred film forming, low Tg, polymers, it wouldbe difficult or impossible to separate the particles while retaining thedesired small particle size. If polymers having higher Tg values wereobtained, separation might be possible but the resultant product wouldbe very dusty and difficult to handle. However, even apart from this, wefind that the viscosifying characteristics of the polymer are reduced ifthe polymer is separated from the aqueous dispersion prior to use.

The polymer is preferably formed from monomers such that, withoutadditional cross linking agent, it has the desired combination ofswellability and insolubility in the water immiscible liquid. However ifa chosen combination of, for instance, polar acrylate monomers andacrylic acid results in the polymer being too swelllable, or perhapseven soluble, then multi-functional cross linking monomer may be addedso as to render the polymer truly cross linked. The cross linkingmonomer will generally be a hydrophobic cross linking monomer such asdiallyl phthalate. Any of the known multi-ethylenically unsaturatedhydrophobic cross linking agents can be used in place of diallylphthalate. The amount of cross linking agent, if added, is generally inthe range 0.01 to 2%, preferably 0.2 to 0.8% by weight of the monomers.In general, we find best results are obtained without the addition ofcross linking agent. It is surprising that substantially linear polymersformed mainly of acrylic or other polar groups are superior to, forinstance, cross linked polymers formed mainly or wholly of hydrophobichydrocarbon groups since it might have been expected that these crosslinked hydrocarbon polymers would have a far greater effectiveness asthickening agents in hydrocarbon or other non-polar liquids.

The aqueous dispersions used in the invention may be made byconventional oil-in-water emulsion polymerisation, for instance bydispersing the monomer or blend of monomers into water in the presenceof an oil-in-water emulsifier or surfactant, for instance using a highspeed Silverson mixer, and may contain an appropriate polymerisationinitiator. Polymerisation may be initiated in conventional manner, forinstance by thermal or redox initiator. Although it is often consideredthat anionic emulsifiers are the most effective in such polymerisations,we have found in the invention that it is particularly desirable to usenon-ionic emulsifiers. These seem to promote the formation of thepreferred particle size distribution. Accordingly a liquid aqueouscomposition according to the invention contains dispersed polymerparticles wherein the polymer is formed from ethylenically unsaturatedmonomers of which at least 80% by weight are hydrophobic and up to 20%by weight are hydrophilic provided that not more than 30% of themonomers are aromatic, the particles are water insoluble polymerparticles having a dry, weight average, particle size of below 10 μm andare insoluble but swellable by water immiscible liquids, and thecomposition contains 2 to 20%, by weight based on the weight of polymer,of a non-ionic surfactant.

Suitable non-ionic surfactants are alkoxylates of long chain alcoholsor, preferably, alkoxylates of alkyl phenols, wherein the alkoxy groupsare preferably ethoxy and the alkyl groups are preferably nonyl,although some propoxy substitution is sometimes useful, as sometimes aresubstituted octyl phenols.

The invention includes a method in which the aqueous dispersion ofpolymer particles, made by emulsion polymerisation, is added to thewater immiscible liquid in order to viscosify that liquid.

The water-immiscible liquid can be any hydrophobic solvent having asolubility in water of less than 5% by weight. It may be a chlorinatedhydrocarbon but is generally a mineral oil or other hydrocarbon. It maybe a refined hydrocarbon such as kerosene, white spirit or aviation fuelor may be an unrefined hydrocarbon such as crude oil. It may be the oilof an oil based paint, in order to provide a paint of improved rheology.It is generally non-polar. It may be the continuous phase of a water inoil emulsion.

We have surprisingly found that when adding the aqueous dispersion ofviscosifying polymer particles to the water-immiscible liquid, optimumviscosification sometimes may not occur unless deliberate steps aretaken to ensure contact between the water-immiscible liquid and thepolymer particles. It appears that the desired hydrophilic coatingaround the particles carries a protective water layer and that this mayinhibit viscosification of the water-immiscible liquid unless it isremoved. It may be removed by dehydration, agitation or emulsification.Thus mechanical agitation may be sufficient to achieve optimumviscosification. Alternatively the addition of water-in-oil emulsifier,that may be anionic, non-ionic or cationic, for instance a blend ofanionic and cationic emulsifiers, may be useful. This emulsifier may bepresent either in the dispersion or in the water-immiscible liquid.Dehydrating agent that may be used may be present in thewater-immiscible liquid, for instance calcium chloride may be present.Instead of chemical absorption, the water may also be removed bydistillation. Cosolvent can be used to promote thickening, alone or inconjunction with surfactants.

The total amount of polymer particles that are added is generally in therange 0.3 to 10%, preferably 0.5 to 5% by weight of the totalcomposition. The amount of particles having the preferred size range(e.g., 0.3 to 5 μm) is preferably 0.2 to 7%, most preferably 0.3 to 4%by weight of the total composition.

The invention is of particular value when the water-immiscible liquid isthe continuous phase of a water-in-oil emulsion. The polymer isinsoluble and unswellable in the water phase but rapidly provides thedesired rheology modification, and in particular increasing viscosity,of the organic phase.

Particularly good thickening effects are achieved when inorganicparticulate solid is present in the resultant composition, and inparticular when such solid is dispersed in a water-in-oil emulsion towhich the polymer dispersion is added. Amine-modified bentonite is aconventional thickener for such systems and the combination ofamine-modified bentonite with the polymer dispersions gives particularlygood thickening results. Other particulate solids that give good resultsinclude barytes and drilled rock, such as is present in drilling mudcompositions.

Thickened liquids according to the invention have particularly desirableshear-thinning rheology. They are highly viscous at low shear but areless viscous, but still have useful viscosity, at high shear. A gelstrength is provided by a developed thixotropy which usefully supportssuspended particles. They are therefore extremely valuable asviscosifiers in invert or oil based drilling fluids, completion fluids,packer fluids, stimulation fluids, fracturing fluids lost circulationand pipeline pigging fluids. The compositions are also useful forthickening the oil phase of various dispersions of particles in oil,especially dispersions of dry polymer particles or aqueous polymer gelparticles.

The following are examples of the invention.

EXAMPLE 1

An emulsion of 297 parts by weight 2-ethylhexyl acrylate and 3 parts byweight glacial acrylic acid was formed in 300 parts water and 24 partsoil in water surfactant (nonyl phenol ethylene oxide condensate). 165parts water containing 6 parts of the surfactant and 0.4 parts thermallydecomposing free radical initiator (ammonium persulphate) were heated ina rection vessel to 80° C. and the emulsion and a further 0.4 parts freeradical initiator in 30 parts water were separately added to the vesselover a period of 3 hours. After the additions were complete, the vesselwas held at 80° C. for a further 30 minutes and the product was thenallowed to cool to room temperature. The product was a dispersion inwater of polymer particles having weight average dry size of about 0.5μm, and mainly in the range 0.1 to 2 μm, with >30% in the range 0.5 to4μ . The product was designated Sample A in the following examples.

EXAMPLE 2

Various amounts of product A were mixed into kerosene in the presence ofa suitable activator. The results are given in Table 1.

                  TABLE 1                                                         ______________________________________                                        Polymer                                                                       Concen-                                                                       tration        Brookfield Solution Viscosity as a function                    (%             of Spindle Speed (rpm)                                         active)                                                                              Spindle 0.5      1.0    5.0   20.0  100.0                              ______________________________________                                        7.5    6       230,000  140,000                                                                              96,000                                                                              16,500                                                                              5150                               5.0    6       64,000   38,000 14,000                                                                              2,600 810                                2.5    3       14,000   12,000  9,600                                                                              2,250 720                                ______________________________________                                    

The results show the remarkable thickening effect which such polymershave in hydrophobic solvents. The apparent viscosity is also verydependent upon the shear rate used during viscosity measurement.

EXAMPLE 3

A drilling fluid is formed of

    ______________________________________                                        Low toxicity mineral oil                                                                             224    mls                                             21.4% CaCl.sub.2 Solution                                                                            72.1   g                                               Emulsifier             7      g                                               Fluid Loss Agent       10     g                                               Lime                   5      g                                               Wetting Agent          1      cc                                              Barite                 243    g                                               ______________________________________                                    

The mud characteristics of 3 such drilling fluids were determined. Onefluid had no additive. Another fluid included 1.5% active polymer ofProduct A. Another fluid contained 3% organophilic clay, but thissuffered from the disadvantage that it required extended mixing toachieve full activation. The results are given in Table 2.

                  TABLE 2                                                         ______________________________________                                        PV         YP          AV      Gels    EBV                                    Additive                                                                              (cP)   (lb/100 ft.sup.2)                                                                         (cP)  10"  10'  (volts)                            ______________________________________                                        None    15     -0.5        14.75  2    2   324                                Product A                                                                             34     33          50.5  19.5 29   744                                Clay    42     22          53    16   29   843                                ______________________________________                                    

The beneficial effect of Product A is clearly apparent.

EXAMPLE 4

A drilling fluid was prepared in the manner described in Example 3. Twoproducts, base on styrene/butadiene resins, which are recommended asviscosity modifiers for oil based drilling fluids were evaluated incomparison with Product B. This product was prepared in the mannerdescribed in Example 1 for Product A except that only 12 parts ofsurfactant were used during the preparative stage. When examined underan optical microscope, the Polymul products appeared substantially freeof particles above 0.5 μm and appeared not to be swollen significantly.

Each product was evaluated at a dose of 1.5% active polymer. The resultsare given in Table 3.

                  TABLE 3                                                         ______________________________________                                                             YP                                                       Unswollen            (lbs/                                                    Particle      PV     100    AV   GELS    EBV                                  Additive                                                                             Size μm (cP)   ft.sup.2)                                                                          (cP) 10"  10'  (volts)                          ______________________________________                                        Product                                                                              >40% 0.5-4 47     75   84.5 27   40   689                              Polymul                                                                              <.5        52     2.5  53.25                                                                              3    4    503                              HV                                                                            Polymul                                                                              <.5        26     0    26   2    2    473                              LV                                                                            ______________________________________                                    

The superior effectiveness of Product B can clearly be seen.

EXAMPLE 5

A drilling fluid was prepared in the manner described in example 3. Thecharacteristics of drilling fluids containing the following viscosifiersat doses of 5 ppb active polymer were determined.

C is a copolymer of 2-ethyl hexyl acrylate: acrylic acid 99:1

D is a copolymer of 2-ethyl hexyl acrylate: acrylic acid 99:1,cross-linked with 500 ppm diallyl phthalate.

E is a terpolymer of 2-ethyl hexyl acrylate: n-butyl-acrylate: acrylicacid 84:15:1

F is a terpolymer of 2-ethyl hexyl acrylate:lauryl methacrylate:acrylicacid 79:20:1

G is a terpolymer of 2-ethyl hexyl acrylate:stearyl methacrylate:acrylicacid 79:20:1

H is a copolymer of N-decyl acrylamide: acrylic acid 99:1

I is 2-ethyl hexyl acrylate

J is a terpolymer of 2 ethyl hexyl acrylate: lauryl methacrylate:acrylic acid 50:49:1

K is 19% vinyl versatate, 80% 2 EHA, 1% acrylic acid

L is 39% vinyl versatate, 60% 2 EHA, 1% acrylic acid

M is 99% 2 EHA, 1% acrylamide

N is 99% 2 EHA, 1% hydroxypropyl acrylate

    ______________________________________                                        PV        YP        AV     GEL       EBV                                      Product                                                                              (cP)   (lb/100 ft.sup.2)                                                                       (cP) 10"    10'  (volts)                              ______________________________________                                        C      51     80        91   39     50   946                                  D      36     15        43.5 4      22   983                                  E      34     19        43.5 2.5     3   691                                  F      75     75        112.5                                                                              34     51   --                                   G      53     49        77.5 16     28   --                                   H      45      4        47   3       3   639                                  I      33     10        38   4      21   784                                  J      49      8        53   2       2   765                                  K      43     54        70   23     44   1146                                 L      45.5   53        72   25     36   1082                                 M      45     18        54   7      28   1204                                 N      39.5   22        50.5 10     30   1219                                 Blank  21     -4        19   1        1.5                                                                              350                                  ______________________________________                                    

Comparison of C with I shows the benefit of including acrylic acid.Comparison of C with D shows that when the polymer is otherwisesatisfactory, it is undesirable to crosslink. Comparison of J with Fshows that including too much of a very long chain methacrylate isundesirable as it appears to make the product too swellable and tendingtowards solubility. The best results are those for products C, F, and Jto N. However all the products shown in the table do give usefulproperties.

EXAMPLE 6

Solid polymer was extracted from Product A by drying overnight at 95° C.The resultant polymer dried into a lump.

Three drilling fluids were prepared according to the recipe in Example3. Product A was added to one of them. The dried polymer obtained fromProduct A was added to another. To a third, the dried polymer wasincorporated into the mineral oil of the drilling fluid for 24 hoursbefore incorporating the other ingredients of the drilling fluid (togive time for swelling of the polymer by the oil). The properties of thedrilling fluid to which Product A had been added were very satisfactory.The properties of the drilling fluid prepared by adding dried polymer tothe oil for 24 hours before adding the other ingredients were very muchworse, and the properties of the drilling fluid to which dried polymerhad been added at the time of mixing the other ingredients were evenworse. This demonstrates the value of maintaining the polymer asdiscrete particles in the aqueous dispersion in which they are formed,in preference to separating the particles from the dispersion.

EXAMPLE 7

A further use of the invention is to increase the stability due tosettlement of dispersions of water soluble polymer particles such aspolyacrylamides in an organic continuous phase, such as a mineral oil.Thus, 500 g of a 50% w/w slurry of polyacrylamide microbeads (20-50 μmin diameter) in Pale Oil 60 was prepared by suspension polymerisation.32.9 g of 38% oil-in-water emulsion of a 99/1 2-ethylhexylacrylate/acrylic acid copolymer and 10 g Tween 81 (Trade mark, sorbitanmonooleate with 5 ethylene oxide units) was added to the slurry withvigorous stirring. The resultant product was a mobile viscous slurrywhich rapidly dispersed in water to give a 1% polyacrylamide solution.No signs of settlement or separation were observed over a period of 21days compared with marked settlement within 24 hours of a productprepared in the absence of the polymer emulsion.

We claim:
 1. A water-immiscible liquid thickened by water insolublepolymer particles having a dry weight average particle size of below 10μm and that are insoluble in the water-immiscible liquid but are swollenby the liquid and that comprise a polymer which has a glass transitiontemperature of less than about 25° C. and formed from monomers of which80-100% are hydrophobic and 0-20% are hydrophilic, in which at least 25%of the monomers are both polar and hydrophobic and in which not morethan 30% of the monomers are hydrophobic aromatic hydrocarbon monomers,all percentages being by weight of total monomer.
 2. A liquid accordingto claim 1 in which the particles are swollen to 4 to 50 times their dryvolume.
 3. A liquid according to claim 1 in which at least 30% by weightof the particles have an unswollen size of 0.05 to 5 μm.
 4. A liquidaccording to claim 1 in which the polymer is formed from 80 to 100%C₁₋₃₀ alkyl (meth) acrylate monomers of which 50% to 100% are C₆₋₁₈alkyl (meth) acrylate monomers, and 0 to 20%, by weight hydrophilicmonomers.
 5. A liquid according to claim 1 in which the polymer isformed from 90 to 100% alkyl (meth) acrylate of which at least 50% byweight is C₆₋₁₀ alkyl (meth) acrylate, and 0.5 to 10%, by weight watersoluble monomer.
 6. A liquid according to claim 1 in which the particlesare formed of a copolymer of ethylenically unsaturated monomers and havean external hydrophilic shell formed of a monomer that is hydrophilicbut that is miscible with the other monomer or monomers in thecopolymer.
 7. A liquid according to claim 1 in which the polymer isformed from monomers that include 0.1 to 5% of a hydrophilic monomerselected from unsaturated carboxylic acids, acrylamide,dialkylaminoalkyl (meth) acrylates and hydroxyalkyl (meth) acrylates. 8.A liquid according to claim 1 in which the polymer is substantiallyuncross-linked.
 9. A liquid according to claim 1 in which the polymerhas a glass transition temperature of less than -20° C.
 10. A liquidaccording to claim 1 in which the polymer is film forming at 20° C. 11.A liquid according to claim 1 in which the polymer particles have beenformed by emulsion polymerisation.
 12. A liquid according to claim 1 inwhich the polymer particles have been made by emulsion polymerisationand the liquid has been formed by adding to the water-immiscible liquidthe resultant aqueous emulsion of the polymer particles.
 13. A liquidaccording to claim 1 and that is a downhole fluid that is a water-in-oilemulsion.
 14. A liquid according to claim 1 in which at least 50% of themonomers are both polar and hydrophobic.
 15. A liquid according to claim14 in which at least 80% of the monomers are both polar and hydrophobic.16. A liquid according to claim 1 that is the continuous phase of adispersion of polymer particles.
 17. A liquid according to claim 1 inwhich the polar and hydrophobic monomers are ethylenically unsaturatedmonomers carrying a carboxylic ester group or amine group substituentand that have a solubility of below 3% by weight in water at 20° C. 18.A liquid according to claim 1 in which the hydrophobic monomers areselected from ethylene and polar hydrophobic monomers which areethylenically unsaturated monomers carrying a carboxylic ester group oramide group substituent and that have a solubility of below 3% by weightin water at 20° C.
 19. A liquid according to claim 1 in which thehydrophilic monomers are selected from dialkyl amino alkyl (meth)acrylate and their quaternary addition and acid salts, acrylamide,N-(dialkyl amino alkyl) acrylamide and meth acrylamide and theirquaternary addition and acid salts, hydroxy alkyl (meth) acrylates andunsaturated sulphonic or carboxylic acids and their alkyl amino salts.20. A liquid according to claim 1 in which the polymer is formed from40-100% 2-ethyl hexyl acrylate, 0-10% hydrophilic groups and 0-50% C₆₋₃₀alkyl (meth) acrylates.
 21. A liquid according to claim 1 in which thepolymer is formed from 40-100% 2-ethyl hexyl acrylate, 0-10% hydrophilicgroups and 0-50% C₁₂₋₁₈ alkyl (meth) acrylates.
 22. A liquid accordingto claim 1 in which the monomers include 0.3-3% acrylic acid.
 23. Aliquid according to claim 5 in which the C₆₋₁₀ alkyl (meth) acrylate is2-ethyl hexyl acrylate.
 24. A liquid according to claim 7 in which theunsaturated carboxylic is acrylic acid.
 25. A liquid according to claim12 in which the emulsion polymerisation was conducted in the presence ofa nonionic oil-in-water emulsifier.
 26. A liquid according to claim 12in which water has been removed from around the said water insolublepolymer particles after addition of the aqueous emulsion to thewater-immiscible liquid.
 27. A liquid according to claim 1 in which theliquid has been formed by adding to the water-immiscible liquid anemulsion of the polymer particles.
 28. A water-immiscible liquidthickened by water insoluble polymer particles having a dry weightaverage particle size of below 10 μm and that are insoluble in thewater-immiscible liquid but are swollen to 4 to 50 times their dryvolume by the liquid, and that comprises a polymer which has a glasstransition temperature of less than about 25° C., said polymer particleshaving been made by emulsion polymerisation of from 80 to 100% C₁₋₃₀alkyl (meth)acrylate monomers of which 50 to 100% are hydrophobic C₆₋₁₈alkyl (meth)acrylate monomers and 0 to 20% are hydrophilic monomers, inwhich at least 25% of the monomers are both polar and hydrophobic, andin which not more than 30% of the monomers are hydrophobic aromatichydrocarbon monomers, all percentages being by weight of total monomer,and said liquid having been formed by adding to the water-immiscibleliquid the resultant aqueous emulsion of the polymer particles.